Wireless networks, for example, Worldwide Interoperability for Microwave Access (WiMAX) networks, provide different types of services to portable devices, e.g., mobile stations (MSs), which receive wireless signals from the network's base stations (BSs). One of these services is a multicast/broadcast service (MBS), through which the network multicasts or broadcasts messages, called advertisements, to one or more MSs covered by the service. A service area in which a service is provided to MSs can be divided into two or more coverage areas, such that different sets of BSs cover different coverage areas. For instance, to provide MBS, an MBS service area may be divided into two or more different coverage areas, each called an MBS zone. An MBS zone is a logical collection of coverage areas of a set of BSs which synchronize with each other and provide simultaneous and similar multicast/broadcast advertisements to MSs covered by that set of BSs. The set of BSs covering one or more MBS zones may be synchronized via a central controller station, called an MBS controller. MBS can be provided to an MS in an idle mode, in which, unlike in an active mode, the MS listens to wireless signals intermittently. An idle MS within an MBS zone receives information about the timing of the synchronized advertisements in that MBS zone and therefore can synchronize the MS's listening intervals with BS's intervals for sending the advertisements.
Mobile stations move from one location to another. As long as an MS relocates within the same MBS zone, because the MS is already synchronized with the BSs in that MBS zone, the MS will continue receiving the advertisements seamlessly. However, when an MS relocates to a new MBS zone, the new MBS zone could have a different set of MBS parameters, e.g., different timings for its advertisements. In this case, the relocated MS must be “handed off” to the new MBS zone by, for example, receiving information about the MBS parameters of the new MBS zone, such that the MS continues receiving the advertisements in the new MBS zone. If the MBS controller detects the relocation in advance, it can prepare for the handoff and provide the new information to the idle MS in time, such that the MS can synchronize with the new MBS zone and receive advertisements in that zone with little delay, thus experiencing a smooth handoff.
When an MS is in active mode, the active MS registers and regularly communicates with a “serving BS” which covers that MS. Thus, the location of an active MS is known to be within the coverage area of its serving BS. If a service is provided to active MSs, when an active MS relocates from one coverage area to another, such relocation is detected because the location of the active MS is known to the network. However, maintaining an MS in an active mode, compared to an idle mode, increases energy consumption and thus undesirably increases usage of the MS's battery. An MS in idle mode, on the other hand, consumes less energy. Therefore, some services, like MBS, do not require an MS to be in active mode and are provided to idle MSs. A mechanism for paging an idle MS has been described in IEEE Std. 802.16e-2005 titled “Air Interface for Fixed and Mobile Broadband Wireless Access Systems,” the contents of which are incorporated herein by reference. However, a new mechanism is needed to prepare for and to perform a handoff of an idle MS from one MBS zone to another.